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Ge-on-Si PIN-photodetectors with Al nanoantennas: The effect of nanoantenna size on light scattering into waveguide modes (2016)

Inga A. Fischer, Lion Augel, Timo Kropp, Songchai Jitpakdeebodin, Nuno Franz, Filipe Oliveira, Erlend Rolseth, Tobias Maß, Thomas Taubner and Jörg Schulze

American Institute of Physics (AIP)

In: Applied Physics Letters

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Publication Date: 2016-02-20

Description: Metallic nanoantennas can be used to enhance the efficiency of optical device operation by re-distributing electromagnetic energy. Here, we investigate the effect of a random distribution of disc-shaped Al nanoantennas of different diameters deposited on Ge-on-Si PIN-photodetectors on the wavelength-dependent responsivity. We compare our experimental results to simulations and find that the largest responsivity enhancement is obtained for wavelengths that correspond to energies at or below the bandgap energy of Ge. We argue that this is the result of antenna-mediated scattering of light into waveguide modes within the Ge-on-Si PIN-photodetectors, which is effectively influenced by nanoantenna size, and we discuss a possible application of the concept for integrated biosensing.

Print ISSN: 0003-6951

Electronic ISSN: 1077-3118

Topics: Physics

Published by American Institute of Physics (AIP)

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Compositional dependence of the band-gap of Ge1−x−ySixSny alloys (2016)

Torsten Wendav, Inga A. Fischer, Michele Montanari, Marvin Hartwig Zoellner, Wolfgang Klesse, Giovanni Capellini, Nils von den Driesch, Michael Oehme, Dan Buca, Kurt Busch and Jörg Schulze

American Institute of Physics (AIP)

In: Applied Physics Letters

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Publication Date: 2016-06-15

Description: The group-IV semiconductor alloy Ge 1− x − y Si x Sn y has recently attracted great interest due to its prospective potential for use in optoelectronics, electronics, and photovoltaics. Here, we investigate molecular beam epitaxy grown Ge 1− x − y Si x Sn y alloys lattice-matched to Ge with large Si and Sn concentrations of up to 42% and 10%, respectively. The samples were characterized in detail by Rutherford backscattering/channeling spectroscopy for composition and crystal quality, x-ray diffraction for strain determination, and photoluminescence spectroscopy for the assessment of band-gap energies. Moreover, the experimentally extracted material parameters were used to determine the SiSn bowing and to make predictions about the optical transition energy.

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Electronic ISSN: 1077-3118

Topics: Physics

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Phase transition and metallization of FeO at high pressures and temperatures (2011)

Rebecca A. Fischer, Andrew J. Campbell, Oliver T. Lord, Gregory A. Shofner, Przemyslaw Dera and Vitali B. Prakapenka

Wiley-Blackwell

In: Geophysical Research Letters

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Publication Date: 2011-12-16

Description: Wüstite, Fe1-xO, is an important component in the mineralogy of Earth's lower mantle and may also be a component of the core. Therefore its high pressure-temperature behavior, including its electronic structure, is essential to understanding the nature and evolution of Earth's deep interior. We performed X-ray diffraction and radiometric measurements on wüstite in a laser-heated diamond anvil cell, finding an insulator-metal transition at high pressures and temperatures. Our data show a negative slope for this apparently isostructural phase boundary, which is characterized by a volume decrease and emissivity increase. The metallic phase of FeO is stable at conditions of the lower mantle and core, which has implications for the high P-T character of Fe-O bonds, magnetic field propagation, and lower mantle conductivity.

Print ISSN: 0094-8276

Electronic ISSN: 1944-8007

Topics: Geosciences , Physics

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Origin of deep subgap states in amorphous indium gallium zinc oxide: Chemically disordered coordination of oxygen (2014)

S. Sallis, K. T. Butler, N. F. Quackenbush, D. S. Williams, M. Junda, D. A. Fischer, J. C. Woicik, N. J. Podraza, B. E. White Jr., A. Walsh and L. F. J. Piper

American Institute of Physics (AIP)

In: Applied Physics Letters

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Publication Date: 2014-06-12

Description: The origin of the deep subgap states in amorphous indium gallium zinc oxide (a-IGZO), whether intrinsic to the amorphous structure or not, has serious implications for the development of p -type transparent amorphous oxide semiconductors. We report that the deep subgap feature in a-IGZO originates from local variations in the oxygen coordination and not from oxygen vacancies. This is shown by the positive correlation between oxygen composition and subgap intensity as observed with X-ray photoelectron spectroscopy. We also demonstrate that the subgap feature is not intrinsic to the amorphous phase because the deep subgap feature can be removed by low-temperature annealing in a reducing environment. Atomistic calculations of a-IGZO reveal that the subgap state originates from certain oxygen environments associated with the disorder. Specifically, the subgap states originate from oxygen environments with a lower coordination number and/or a larger metal-oxygen separation.

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Electronic ISSN: 1077-3118

Topics: Physics

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Axisymmetric circulation driven by marginal heating in ice-covered lakes (2015)

G.B. Kirillin, A.L. Forrest, K. Graves, A. Fischer, C. Engelhardt, B.E. Laval

Wiley-Blackwell

In: Geophysical Research Letters

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Publication Date: 2015-04-01

Description: Below the temperature of maximum density (TMD) in freshwater lakes, heating at the lateral margins produces gravity currents along the bottom slope, akin to katabatic winds in the atmosphere and currents on continental shelves. We describe axisymmetric basin-scale circulation driven by heat flux at the shorelines in polar Lake Kilpisjärvi. A dense underflow originating near the shore converges towards the lake center, where it produces warm upwelling and return flow across the bulk of lake water column. The return flow, being subject to Coriolis force, creates a lake-wide anticyclonic gyre with velocities of 2-4 cm s -1 . While warm underflows are common on ice-covered lakes, the key finding is the basin-scale anticyclonic gyre with warm upwelling in the core. This circulation mechanism provides a key to understanding transport processes in (semi-) enclosed basins subject to negative buoyancy flux due to heating (or cooling at temperatures above TMD) at their lateral boundaries.

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Electronic ISSN: 1944-8007

Topics: Geosciences , Physics

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A multi-state magnetic memory dependent on the permeability of Metglas (2015)

J. R. Petrie, K. A. Wieland, J. M. Timmerwilke, S. C. Barron, R. A. Burke, G. A. Newburgh, J. E. Burnette, G. A. Fischer and A. S. Edelstein

American Institute of Physics (AIP)

In: Applied Physics Letters

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Publication Date: 2015-04-09

Description: A three-state magnetic memory was developed based on differences in the magnetic permeability of a soft ferromagnetic media, Metglas 2826MB (Fe 40 Ni 38 Mo 4 B 18 ). By heating bits of a 250 nm thick Metglas film with 70–100 mW of laser power, we were able to tune the local microstructure, and hence, the permeability. Ternary memory states were created by using lower laser power to enhance the initial permeability through localized atomic rearrangement and higher power to reduce the permeability through crystallization. The permeability of the bits was read by detecting variations in an external 32 Oe probe field within 10 μ m of the media via a magnetic tunnel junction read head. Compared to data based on remanent magnetization, these multi-permeability bits have enhanced insensitivity to unexpected field and temperature changes. We found that data was not corrupted after exposure to fields of 1 T or temperatures of 423 K, indicating the effectiveness of this multi-state approach for safely storing large amounts of data.

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High-Pressure, High-Temperature Equations of State Using Nanofabricated Controlled-Geometry Ni/SiO2/Ni Double Hot-Plate Samples (2015)

Jeffrey S. Pigott, Derek A. Ditmer, Rebecca A. Fischer, Daniel M. Reaman, Rostislav Hrubiak, Yue Meng, Robert J. Davis, Wendy R. Panero

Wiley-Blackwell

In: Geophysical Research Letters

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Publication Date: 2015-11-26

Description: We have fabricated novel controlled-geometry samples for the laser-heated diamond anvil cell (LHDAC) in which a transparent oxide layer (SiO 2 ) is sandwiched between two laser-absorbing layers (Ni) in a single, cohesive sample. The samples were mass manufactured (〉10 4 samples) using a combination of physical vapor deposition, photolithography, and wet and plasma etching. The double hot-plate arrangement of the samples, coupled with the chemical and spatial homogeneity of the laser-absorbing layers, addresses problems of spatial temperature heterogeneities encountered in previous studies where simple mechanical mixtures of transparent and opaque materials were used. Here we report thermal equations of state (EOS) for nickel to 100 GPa and 3000 K and stishovite to 50 GPa and 2400 K obtained using the LHDAC and in situ synchrotron x-ray micro-diffraction. We discuss the inner core composition and the stagnation of subducted slabs in the mantle based on our refined thermal EOS.

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Fabrication of GeSn-multiple quantum wells by overgrowth of Sn on Ge by using molecular beam epitaxy (2015)

F. Oliveira, I. A. Fischer, A. Benedetti, P. Zaumseil, M. F. Cerqueira, M. I. Vasilevskiy, S. Stefanov, S. Chiussi and J. Schulze

American Institute of Physics (AIP)

In: Applied Physics Letters

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Publication Date: 2015-12-29

Description: We report on the fabrication and structural characterization of epitaxially grown ultra-thin layers of Sn on Ge virtual substrates (Si buffer layer overgrown by a 50 nm thick Ge epilayer followed by an annealing step). Samples with 1 to 5 monolayers of Sn on Ge virtual substrates were grown using solid source molecular beam epitaxy and characterized by atomic force microscopy. We determined the critical thickness at which the transition from two-dimensional to three-dimensional growth occurs. This transition is due to the large lattice mismatch between Ge and Sn (≈14.7%). By depositing Ge on top of Sn layers, which have thicknesses at or just below the critical thickness, we were able to fabricate ultra-narrow GeSn multi-quantum-well structures that are fully embedded in Ge. We report results on samples with one and ten GeSn wells separated by 5 and 10 nm thick Ge spacer layers that were characterized by high resolution transmission electron microscopy and X-ray diffraction. We discuss the structure and material intermixing observed in the samples.

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Common climatic signal from glaciers in the European Alps over the last 50 years (2017)

C. Vincent, A. Fischer, C. Mayer, A. Bauder, S. P. Galos, M. Funk, E. Thibert, D. Six, L. Braun, M. Huss

Wiley-Blackwell

In: Geophysical Research Letters

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Publication Date: 2017-01-29

Description: Conventional glacier-wide mass balances are commonly used to study the effect of climate forcing on glacier melt. Unfortunately, the glacier-wide mass balances are also influenced by the glacier's dynamic response. Investigations on the effects of climate forcing on glaciers can be largely improved by analyzing point mass balances. Using a statistical model, we have found that 52% of the year-to-year deviations in the point mass balances of six glaciers distributed across the entire European Alps can be attributed to a common variability. Point mass balance changes reveal remarkable regional consistencies reaching 80% for glaciers less than 10 km apart. Compared to the steady-state conditions of the 1962-1982 period, the surface mass balance changes are -0.85 m w.e. a -1 for 1983-2002 and -1.63 m w.e. a -1 for 2003-2013. This indicates a clear and regionally consistent acceleration of mass loss over recent decades over the entire European Alps.

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